A leading climatologist on the Weather Channel in the United States has caused a squall in the industry by arguing that any weather forecaster who dares publicly to question the notion that global warming is a manmade phenomenon should be stripped of their professional certification.

The call was made by Heidi Cullen, host of a weekly global warming programme on the cable network called The Climate Code, and coincides with a stretch of severely off-kilter weather across the US this winter and moves by Democrats to draft strict new legislation to curb greenhouse gas emissions.

Specifically, Ms Cullen is suggesting that the American Meteorological Society (AMS) revokes the "seal of approval" that it normally extends to broadcast forecasters in the US in cases where they have expressed scepticism about man's role in pushing up planetary temperatures.

"It's like allowing a meteorologist to go on-air and say that hurricanes rotate clockwise and tsunamis are caused by the weather," she wrote in her internet blog. "It's not a political statement... it's just an incorrect statement."

Ms Cullen is not alone in trying to marginalise doubters, who mostly argue that recent rises in temperatures are caused by normal cyclical weather patterns. They were described as "global warming deniers" by former vice-president Al Gore in his recent film An Inconvenient Truth.

Most Americans need neither Mr Gore nor Ms Cullen to know that something is up with the weather, however. This year's "wacky winter", as headline writers now describe it, continues to serve up unsettling surprises, the most recent of which was snow falling on the beach in Malibu, California, on Wednesday. The freeze in western states is expected to have eased by the weekend, but already it may have devastated California's citrus harvest with as much as 75 per cent destroyed by ice and frost. Freezing rain and snow paid a rare visit this week meanwhile to Texas and Oklahoma.

However, it is the eastern states that have experienced the strangest conditions - a six-week period of temperatures far above their normal range for the time of year. The unusual warmth has been a disaster for ski resorts in the area, some struggling even to produce man-made snow that will stick for a second, as well as for retailers trying to sell everything from winter jackets to snow shovels and duvets.

Cherry trees are blossoming in Washington DC and in some parks in New York, where the temperature reached a bewildering 22C (72F) 10 days ago, the daffodils are in full flower. When a few flakes finally fell in Central Park a week ago - so few they could not be measured by instruments - it was the latest recorded snow fall since records began in 1878.

All of this will be political grist to Democrats on Capitol Hill, who are gearing up to take advantage of their new position as the majority party to make climate change a legislative priority.

Nancy Pelosi, the new Speaker of the House, is expected to call for a new select committee purely to devise new laws on combating global warming, probably to be headed by Representative Edward Markey of Massachusetts. "It's an issue that the Speaker thinks is critical to address," her spokeswoman said.

Any new legislation is likely to include mandatory caps on greenhouse gas emissions by American industries, a path that the White House has vigorously refused to follow. Democrats will also explore creating a market in emission caps, similar to the one that already exists in Europe. Under such a system, individual industries would be able to buy exemptions to exceed certain emission limits or acquire them and sell them to other industries.

It is clear that Democrats are intending to seize the issue from under the nose of President George Bush and embarrass him for his refusal to give the issue more credence. However, White House aides have indicated that the President will give climate change an important place in his annual State of the Union address to Congress next Tuesday. But few observers believe he is ready to go as far as some Democrats would like in imposing mandatory emission ceilings.

Extreme weather

COLD

* In California, a state used to mild winter weather, residents of Malibu Beach and West LA woke up to a light dusting of snow on Wednesday. Farmers say the unusually cold temperatures have devastated the state's orange and lemon crop.

* Texas, meanwhile, has seen a vicious ice storm descend across much of the state, causing blanket power cuts and traffic chaos. At least 10 people have been killed in the state since the weekend, thanks to the abnormally cold weather.

* Sixty winter-related deaths have been recorded across nine states in total as moist air coming from the Gulf of Mexico has met head-on with icy Arctic air from Canada, spreading snow storms as far afield as California and Missouri.

WARM

* Eastern America has seen a spell of freakishly warm weather. In early January, New York had record temperatures of 22C as New Yorkers strolled through Central Park in T shirts in a month when the city is usually covered in snow.

* The ski industry in America and Canada has been hard hit by the lack of snow. Although a recent drop in temperatures has finally brought snowfall, ski resorts across the continent have had to make do with artificial snow for much of the season so far.